Method of grease manufacture



March 22., G 5 BRlGHT ET AL METHOD OF GREASE MANUFACTURE Filed May 22, 1963 NW MN United States Patent 3,242,083 METHOD OF GREASE MANUFACTURE Gordon S. Bright, Port Arthur, Herbert J. Pitman, Groves, and Paul A. (look, Nederland, Tera, assignors to Texaco Inc., New York, N.Y., a corporation of Delaware Filed May 22, 1963, Ser. No. 282,434 14 Claims. (Cl. 25241) This invention relates to improvements in grease manufacture and more particularly to an improved low temperature method for the preparation of soap thickened greases. It relates particularly to an improved low temperature method for the preparation of greases thickened with lithium soaps of hydroxy fatty acids.

The so-called low temperature methods of grease preparation comprise saponifying a saponifiable fatty acid material with a metal base in the presence of a portion of the lubricating oil employed in the grease, heating the grease mixture at a higher temperature below the melting point of the soap for dehydration and soap conditioning periods, and then cooling with the addition of the remainder of the lubricating oil employed in the grease. These methods have very important advantages in convenience and economy over the soap melt processes wherein a mixture of lubricating oil and soap is heated at a high temperature above the melting point of the soap for a sufficient time to obtain complete melting of the soap and then cooled by various means, ordinarily at a rapid rate. However, the low temperature methods have the disadvantages of producing generally much lower yields than the soap melt processes and of requiring longer manufacturing times. In addition, greases prepared by low temperature methods are generally inferior in certain respects, particularly in shear stability, as compared with greases obtained by melt-quench processes.

The present invention provides an improved low temperature method for the preparation of soap thickened greases, wherein increased yields and improved product quality are obtained. The method of our invention involves essentially carrying out the saponification step of the grease making process by slowly introducing a solution or slurry of metal base into a recirculating stream of lubricating oil and saponifiable material at an elevated temperature suflicient to produce a rapid reaction between the metal base and the saponifiable material and thereafter subjecting the recirculated stream to turbulent mixing before returning it to the main body of saponification mixture. Very advantageously, the stream may be sub jected to shearing, most suitably by passing it through a shear valve with at least a substantial pressure drop across the valve. The process representing the preferred embodiment of our invention comprises recirculating the grease mixture in the same manner during the subsequent heating at higher temperatures, very advantageously with shearing by means of a shear valve during at least a portion of the further heating step.

The mixture of saponifiable material and lubricating oil is at a temperature at least suflicient to melt the saponifiable material and preferably at a temperature of at least about 160 F. during the addition of the metal base. Ordinarily it is at a temperature between about 180 F. and 200 F. In some cases, it has been found advantageous to carry out the alkali injection with the mixture of saponifiable material and lubricating oil at somewhat higher temperatures, such as in the range of from about 200 to about 220 F.

Lithium hydroxy fatty acid soap thickened greases are obtained in the above manner in yields which are substantially equivalent to those obtained by the meltquench procedure, and having substantially equivalent shear resistance and other properties. Electron micrographs obtained upon these greases show that the manner 3,242,088 Patented Mar. 22, 1966 of carrying out the saponification has a pronounced eifect upon the fiber development, resulting in well formed fibers having a high length to width ratio very similar in appearance to those obtained by certain melt-quench procedures, and substantially diiferent from those in greases obtained by the low temperature method carried out in the same manner except for the alkali being added directly to the initial kettle charge.

While we do not wish to be limited by any particular theory, it is thought that the finer soap fibers obtained when the saponification is carried out by the method of our invention may be due to the effect of the special conditions involved in this operation in promoting the formation of more numerous crystal nuclei. The method involves essentially an incremental saponification reaction wherein the soap molecules are effectively dispersed as soon as they are formed and maintained in a dispersed and relatively dilute solution until the saponification is substantially complete. The method thus provides an effective means of preventing the formation of large agglomerates during the saponification due to insufiicient dispersion and local high concentrations of soap molecules.

A particularly preferred embodiment of our invention comprises carrying out the grease making process following the saponification step by the method of L. F. Badgett, W. R. Hencke and F. T. Crookshank, disclosed and claimed in their copending application 282,330, filed of even date herewith, wherein the grease mixture is recirculated continuously during the heating and cooling steps and additional oil is introduced into the recirculating stream of grease mixture during the cooling step, and preferably during the heating step also. By this method, the above advantages are obtained together with a large reduction in the manufacturing time required.

The figure is a diagrammatic illustration of one form of apparatus suitable for making greases in accordance with the preferred embodiment of this invention.

Referring to more detail to the figure, numeral 1 represents a jacketed grease kettle equipped with stirrer 2 and adapted to be heated to an elevated temperature above about 350 F. In carrying out the grease preparation, the grease kettle is charged with saponifiable material and lubricating oil, the latter in an amount equal to at least about 2 times the weight of the saponifiable material and preferably at least about 3 times the weight of the saponifiable material. The kettle contents are heated with stirring up to a temperature in about the range -220 F. and maintained at such temperature until the metal base employed in the saponification step has been added in the manner described below.

When the saponification mixture has been heated to a temperature in about the range 160-220 F., or during heating up to this temperature if desired, recirculation of the grease mixture around the kettle is begun by turning valves 6 and 8 to the open position and starting pump 12. The grease mixture passes through line 5, containing valve 6, line 10 containing valve 8, pump 12, and line 14 containing pressure gauge 15 and shear valve 19. Lines 5, 10 and 14 may be jacketed or otherwise provided with means for applying additional heating and cooling to the recirculating stream of grease mixture. The shear valve is suitably a gate valve, which is located a sufficient distance from kettle 1 to avoid spraying into the kettle when it is operated under a back pressure. As indicated in FIG. 1, the recycle stream of grease mixture is preferably returned at the top of the grease kettle or at least at a point above the surface of the body of grease mixture within the kettle, in order to increase the evaporation rate during the dehydration. Circulation of the grease mixture through the recycle system may be carried out at a rate such that the weight of recirculated saponification mixture is equal to the total weight of sponification mixture, i.e., one batch turnover, in from about 0.1 to about 15 minutes, preferably in from about 0.25 to about 10 minutes, and ordinarily in from about 0.5 to about minutes.

During the recirculation and while the grease mixture is at a temperature in the range from about 160 F. to about 220 F., a solution of metal base is introduced into the recycle stream from tank 16 until an amount has been added which is substantially equal to that theoretically required to completely react with the saponifiable material. The solution of metal base passes through line 17 containing valve 18 into line 36. From line 36, it passes into the recirculating stream of saponification mixture either at the intake side of pump 12 by passing through valve 37 into line 10, or it may pass into the discharge side of pump 12 by passing through valve 38 into line 14 when valve 19 is in a partly closed position. It is preferably introduced into the stream of saponification mixture at the intake side of pump 12 in order to obtain increased mixing by the action of the pump. When the metal base solution passes into the discharge side of pump 12, and preferably when it passes into the intake of pump 12 also, valve 19 is set in a partly closed position so as to give a pressure drop of about -200 pounds per square inch, and preferably about 25125 pounds per square inch across the valve.

The solution of metal base in tank 16 may comprise a metal base dissolved in any liquid in general which is vaporizable at the temperatures employed in the later heating steps of the grease making process. An aqueous solution of metal base containing water in an amount substantially equivalent to that required to dissolve the metal base is suitably employed for this purpose, although in some cases it may be desirable to employ a substantially higher amount of water as an aid in the saponification. Ordinarily the solution will contain about 1-2 times the amount of water required to completely dissolve the metal base.

The solution of metal base is introduced into the recirculating stream of saponification mixture at a rate such that the ratio of the rate of recirculation of the saponification mixture to the rate of injection of the metal base solution is at least about 10: 1, respectively, and may be as high as about 1,000: 1, respectively. Under the preferred conditions, an aqueous solution of metal base comprising water in an amount from about 1 to 2 times the amount required to completely dissolve the metal base is introduced into the recirculating stream of saponification mixture at a rate such that the ratio of the rate of recirculation of the saponification mixture to the rate of inroduction of the metal base solution is in a ratio from about 20:1 to about 250:1, respectively, and for a minimum period of about minutes.

The particularly preferred conditions for the preparation of greases thickened with lithium soaps of hydroxy fatty acid materials comprise employing a saponification mixture comprising lubricating oil and saponifiable material in a weight ratio from about 4:1 to about 10:1 and an aqueous lithium hydroxide solution comprising water in an amount from about 1 to 1.5 times the amount required to completely dissolve the metal base, and carrying out the saponification with the recycle rate and the rate of alkali injection such as to give at least two batch turnovers of the saponification mixture during the alkali injection.

Following the addition of the metal base solution, the grease mixture obtained is heated to the top temperature employed over a period of time SUfi'lClBIlt to obtain substantially complete dehydration, ordinarily in a period from about 30 minutes to about 4 hours. The maximum temperature to which the grease mixture is heated is ordinarily in the range from just below the melting point of the soap to about 75 F. below the melting point of the soap. In some cases, it may be heated at or even slightly above the melting point of the soap for a period of time which is insuflicient to obtain complete melting of the soap. The heating cycle in the grease preparation ordinarily includes a period of at least about 15 minutes in the top temperature range, such as from about 15 minutes to about 1 hour or longer if desired.

Recycling of the grease mixture in the manner described above in connection with the saponification step may very advantageously be carried out during heating of the grease mixture up to the top temperature, and also during a holding period at the top temperature, if such is employed. The recycling may be carried out with shearing of the grease mixture by means of shear valve 19 during all or a portion of the heating cycle.

Circulation of the grease mixture through the recycle system during the heating cycle following the saponification step is carried out at a rate sufficient to give one batch turnover Within about 22 minutes, such as in about 0.322 minutes, and preferably in about 04-15 minutes, based on the weight of the grease mixture during the heating cycle, or in about 02540 minutes, and preferably 0.3-12 minutes based upon the average Weight of grease mixture during the heating cycle when the process is carried out with additional oil added during the heating step as described hereinbelow. Recycling during the cooling cycle is suitably carried out at a rate sufficient to provide a batch turnover in about 0.5-35 minutes, and preferably in about 1-20 minutes, based on the weight of the finished grease, or in about 0. 427 minutes, and preferably about 0.5-17 minutes, based on the average weight of grease mixture within the kettle during the cooling cycle.

Very advantageously, the recycling is carried out for a minimum period of about 15 minutes, and preferably for at least about 30 minutes, during the heating cycle following the saponification, until at least 5 batch turnovers and preferably at least 10 batch turnovers, based on the average weight of the grease mixture during this period, are obtained. The recycling is preferably carried out continuously throughout the heating cycle following the saponification step.

In carrying out the grease preparation by our preferred method, with recirculation of the grease mixture during the cooling step also, the additional oil employed in the grease is introduced at a substantially lower temperature than the grease mixture into the recirculating stream of grease mixture. The added oil is at a temperature at least about F. and preferably at least about F., below the temperature of the grease mixture at the beginning of the cooling step. This additional lubricating oil passes from tank 20 into line 36 by way of line 22 containing valve 23, pump 24, line 25 and line 26 containing valve 27, dial thermometer 33, pressure gauge 34 and valve 35. Valve 35 is preferably a one way valve, most suitably of a type designed to prevent gravity flow of oil through pump 24 when the pump is not operating, such as a diaphragm controlled reducing valve or a spring loaded check valve. In line 36, the oil may pass into the recirculating stream of grease mixture either at the intake or the discharge side of pump 12 as described hereinabove in connection with the introduction of the metal base solution. It preferably passes into the grease mixture at the intake of pump 12 by passing through valve 37 into line 10. The oil may be introduced into the recirculating stream of grease mixture at a rate such that the ratio of the rate of flow of the grease mixture before the point of confluence to the rate of oil injection is from about 1:1 to about 400: 1, preferably in a ratio from about 2:1 to about 150:1, and most advantageously in a ratio from about 3:1 to about 50:1, by weight, respectively.

The oil addition is preferably commenced at the beginning of the cooling step and may be carried out over the entire cooling period or through only a portion thereof. Additional cooling may be applied to the kettle, and

also to the recirculating stream of grease mixture. The amount of lubricating oil added during the cooling may be from about to as high as about 90 percent of the total oil contained in the grease. It will usually be from about 25 to about 75 percent of the total oil contained in the grease. When the oil addition is carried out during only a portion of the cooling step, it is advantageous in some cases to continue recirculation of the grease mixture with shearing down to the drawing temperature. Any additives employed in the grease are ordinarily added during the cooling step when the grease mixture is at a suitably low temperature, ordinarily at below about 250 F. The cooled grease mixture is finally drawn through line 40 containing valve 41.

The process may be carried out very advantageously with the addition of preheated oil to the grease mixture following the saponification step as a means of bringing the grease mixture rapidly up to the top temperature, the preheated oil being preferably introduced into the recycle line, as also described in the said copending application Serial No. 282,330. In this procedure, the oil passes from tank to heater 30 by way of line 22, pump 24, line and line 28 containing valve 29. Heater 30 may be any suitable type of heater such as a coil heater as indicated in the diagram. From heater 30 the oil passes into line 26 and is introduced into the circulating stream of grease mixture at either the intake or the discharge side of pump 12 as described hereinabove in connection with the introduction of cooling oil. The oil preferably passes into the recirculating stream of grease mixture at the intake of pump 12 except when a relatively light oil is employed which might cause vapor locking in the pump at the temperature of the injected oil and of recirculated grease mixture. The temperature of the oil added in this manner is preferably substantially higher than that of the grease mixture, and may be up to or even slightly higher than the melting point of the soap in some cases. The rate at which this oil is introduced may suitably be such that the ratio of the rate of recirculation of the grease mixture to the rate of oil injection is within the ranges disclosed hereinabove in connection with the introduction of cold oil during the cooling cycle. The amount of oil step, may be carried out by circulating the grease mixture through shear valve 19 set to give a pressure drop of about 20200, and preferably 25-125 pounds .per square inch. Shearing of the recycle stream is preferably carried out during oilv addition during the cooling, and also during oil addition in the heating step where such oil addition is employed. Lithium hydroxy fatty acid soap thickened greases are obtained in this manner in improved yields and with other advantages in this manner without the necessity of milling. However, greases prepared in accordance with our invention either with or without shearing in the above manner following the saponification step may be finished by milling in the conventional manner if desired.

The metal base employed in the saponifica'tion may be a hydroxide or other suitable compound of any of the metals ordinarily employed as the metal component of the soap in the preparation of lubricating greases, such as sodium, lithium, potassium, calcium, barium, magnesium, Zinc, cobalt, manganese, aluminum, lead, etc., as well as mixtures of two or more metals. It is preferably a metal oxide, hydroxide or carbonate. The grease prep ii arations which are most advantageously carried out by the method of this invention are those wherein a lithium base, or a mixture thereof with a different metal base is employed as the saponifying agent.

Suitable saponifiable materials employed in these grease preparations are higher fatty acids containing from about 12 to 32 carbon atoms per molecule and hydroxy substituted. higher fatty acids, and glycerides and other esters and mixtures thereof. In the grease preparations wherein the method of our invention is employed most advantageously, the saponifiable material comprises at least about 35 percent, and preferably at least about 50 percent by weight of a hydroxy fatty acid material. A particularly suitable class of saponifiable materials for this purpose are the lower alkyl (C ester of 12-hydroxystearic acid.

The oleaginous liquids employed in these greases may be any suitable oils of lubricating characteristics, including the conventional mineral lubricating oils or synthetic oils obtained by various refining procedures such as cracking and polymerization, and other synthetic oleaginous compounds such as high molecular weight ethers and esters. The di-carboxylic esters such as di-Z-ethylhexyl sebacate, di(secondary amyl) sebacate, di-Z-ethylhexyl azelate, di-isooctyl adipate, etc., and a particularly suitable class of synthetic oils and may be employed as the sole oleaginous component of the grease or' in conjunction with other synthetic oils or mineral oils. However, the oil employed in the saponification mixture is preferably one which is substantially inert under the saponification conditions, most suitably a mineral lubricating oil. Suitable mineral oils for use in these greases are those having viscosities in the range from about seconds to about 2,000 seconds Saybolt Universal at 100 F. and may be either naphthenic or paraflinic in type, or blends of the two.

The following example is illustrative of lubricating grease preparations carried out by a method representing a preferred embodiment of this invention.

Example I A lithium 12-hydroxystearate grease was prepared as described below.

The following materials were employed in this preparation: The lubricating oil employed was a blend comprising 65 percent by weight of a deasphalted and steam reduced parafiinic residual oil having a Saybolt Universal viscosity at 210 F. of about 160 seconds, and 35 percent by weight of a refined parafiinic distillate oil having a Saybolt Universal viscosity at 100 F. of about 184 seconds. The saponifiable material employed was a commercially obtained methyl ester of 12-hydroxystearic acid, having a saponification number of 181, an acid number of 1.6, an iodine number of 4 and a titer of 68.1 C. The saponifying agent was an aqueous solution of lithium hydroxide, containing 9.29 percent by weight of lithium hydroxide and 0.06 percent by weight of lithium carbonate, by analysis.

The equipment employed in the grease preparation was a pound capacity steam heated laboratory kettle with auxiliary equipment for circulation of the kettle contents and for injection of alkali solution and of hot and cold oil into the circulating stream as shown in FIG. 1. The circulation equipment consisted of a 1% inch pipe connecting the kettle drawotf with a Viking Model GX151 pump operated by a variable drive giving a circulation rate of 0.6-6.0 gallons per minute, and a inch pipe extending from the pump to the top of the kettle and containing a shear valve, the recycle lines being jacketed and steam heated.

Following is a detailed description of the method employed in the grease preparation: The grease kettle was charged with 37 pounds of the lubricating oil blend and 7.4 pounds of methyl l2-hydroxystearate, and the mixture heated in the kettle with stirring to about F Circulation of the kettle contents through the recycle line was then begun at a rate of 2.0 gallons per minute, with the shear valve set so as to give a pressure .drop of 60 pounds per square inch across the valve, with continued heating and stirring in the kettle. When the temperature of the mixture was about 180 F., 7.44 pounds of the aqueous lithium hydroxide solution were introduced into the recirculating stream at a uniform rate during 19 minutes, while the temperature of the kettle contents was in the range from 180 F. to 200 F. The grease mixture was then heated to 325 F. in about 1 hour, and 25.9 pounds of the oil blend, preheated to about 310 F., were injected into the recirculating stream of grease mixture in about 33 minutes, while the temperature of the grease mixture was maintained at about 325-335. The grease mixture was then held at about 330-335 for an additional /2 hour. Thereafter, the heat to the kettle and to the recycle line was cut off and cooling begun with the injection of 49.2 pounds of the oil blend at ambient temperature into the recirculating stream of grease mixture in about /2 hour, with the shear valve set at 60 pounds pressure drop. When the grease mixture had cooled to 230 F., 0.6 pound of diphenylamine was added and the recirculation with shearing continued down to the drawing temperature of about 200 F. The grease was finished by milling with one pass through a Premier Colloid Mill set at 0.003 inch clearance. The total time required for the grease preparation was 3 hours and 58 minutes.

The product obtained as described above was a smooth grease obtained in a good yield and having very satisfactory lubricating properties generally, including particularly a high shear stability for a lithium hydroxy fatty acid soap thickened grease. Following are analytical data and test results obtained upon this grease.

Composition, percent:

Lithium l2-hydroxystearate 6.4 Free LiOH 0.08 Free fatty acid None Free neutral fat 0.25 Water 0.05 Lubricating oil Remainder Dropping point, ASTM, F 392 Penetration, ASTM at 77 F.:

Worked, 60 strokes 269 Worked, 10,000 strokes 286 Worked, 40,000 strokes 292 Worked, 70,000 strokes 298 Worked, 100,000 strokes 304 Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim: 1. In a process for preparing a soap thickened grease comprising the steps of saponifying a saponifiable fatty acid material with a metal base in the presence of at least a portion of the lubricating oil contained in the grease, heating the grease mixture thus obtained at a higher temperature below the melting point of the soap and finally cooling the grease mixture and adding any additional lubricating oil employed in the grease, the improvement which comprises initially providing a mixture of lubricating oil and saponifiable material at an elevated temperature suificient to obtain a reaction between the said saponifiable material and said metal base, and carrying out the saponification by continuously withdrawing a minor stream from a maintained body of the said mixture in a grease making zone, continuously adding to the said withdrawn stream a solution of metal base in a liquid which is vaporizable at a temperature employed in the grease making process, subjecting the resulting combined stream to turbulent mixing and then returning it to the said maintained body of saponifiable material and oil mixture, said solution of metal base being added at a rate such that the ratio of the rate of recirculation of the said mixture of lubricating oil and saponifiable material to the rate of addition of the said metal base solution is at least about 10: 1.

2. The process of claim 1 wherein the introduction of the said metal base solution is carried out over a period of at least about 15 minutes and with recirculation of the said mixture at a rate suficient to give at least 2 batch turnovers during the introduction of the said metal base solution.

3. The process of claim 1 wherein the said withdrawn stream of mixture after the addition of the said solution of metal base is passed through a shear valve with a pressure drop across the said valve of about 10200 pounds per square inch before the said stream is returned to the said maintained body of mixture.

4. The process of claim 3 wherein the pressure drop across the said valve is about 25-125 pounds per square inch.

5. The process of claim 1 wherein the grease mixture is circulated following the saponification up to the initiation of the cooling step at a rate such that the weight of recirculated grease mixture is equal to the total average weight of said mixture during the heating step in from about 0.25 to about 15 minutes.

6. The process of claim 5 wherein said mixture is circulated at a rate such that the weight of recirculated mixture is equal to the total average weight of mixture in from about 0.3 to about 12 minutes.

7. The process of claim 1 wherein said solution of metal base is an aqueous solution comprising water in an amount from about 1 to about 2 times that required to completely dissolve the said metal base.

8. The process of claim 1 wherein the said saponification material comprises at least about 50 percent by weight of a hydroxy fatty acid material.

9. The process of claim 1 wherein the said metal base is an aqueous solution of lithium hydroxide.

10. The process of claim 1 wherein said mixture comprises lubricating oil and saponifiable material in a weight ratio from about 4:1 to about 10:1, respectively.

11. The process of claim 1 wherein the said cooling step is carried out with the addition of about 25-75 percent of the total oil contained in the grease at a substantially lower temperature than the grease mixture, the cooling step being carried out with recirculation of the grease mixture around the said grease making zone by continuously withdrawing a minor stream from a maintained body of grease mixture Within the said grease making zone and continuously returning the said withdrawn stream to the said grease making zone and carrying out the oil addition during the said cooling step by introducing the added oil into the recirculation stream of grease mixture and passing the combined stream of grease mixture and adding lubricating oil through a shear valve with a pressure drop across the said valve of about 10-200 pounds per square inch before returning the said combined stream to the said grease making zone, the rate of said recirculation of grease mixture and of oil addition being in a ratio from about 1:1 to about 400:1, respectively.

12. In a process for preparing a lithium soap thickened grease comprising the steps of saponifying a saponifiable fatty acid material comprising at least a major portion of a hydroxy fatty acid material with a lithium base in the presence of at least a portion of the lubricating oil contained in the grease, heating at a higher temperature below the melting point of the soap and finally cooling the grease mixture thus obtained and adding any additional lubricating oil contained in the grease, the improvement which comprises initially providing a mixture of lubricating oil and saponifiable material in a ratio from about 4:1 to about 10:1, respectively, at a temperature in the range from about 160 F. to about 200 F., and carrying out the saponification with recirculation of the said grease mixture by continuously withdrawing a minor stream from a maintained body of the said grease mixture in a grease making zone, continuously adding to the said withdrawn stream an aqueous solution of a lithium base comprising lithium base and water in an amount from about 1 to 2 times the amount required to completely dissolve the said lithium base, passing said withdrawn stream together with said solution of lithium base through a shear valve with a pressure drop of about 25-125 pounds per square inch across the said valve and then returning the stream to the said maintained body of mixture, said mixture being recirculated at a rate such that the amount of recirculated grease mixture is equal to the total weight of the said mixture in from about 0.1 to about 15 minutes, the rate of recirculation of the said mixture of lubricating oil and saponifiable material to the rate of addition of the said solution of lithium base being in a ratio from about 10:1 to about l,000:1, respectively.

13. The process of claim 12 wherein said saponifiable material is a lower alkyl ester of 12-hydroxy fatty acid. 14. The process of claim 12 wherein the said lithium base solution comprises lithium hydroxide and water in a weight ratio from about 1:5 to about 1:6, respectively.

References Cited by the Examiner UNITED STATES PATENTS 2,332,202 '10/ 1943 Calkins 252-42.1 2,450,220 9/1948 Ashburn et al 252-41 2,830,022 4/1958 Nelson et al. 252-41 2,870,090 1/1959 Pitrnan et a1 252-39 2,886,525 5/1959 Dilworth et al. 252-39 3,015,624 1/1962 Hencke et al. 252-41 3,018,249 1/1962 Morway et al 252-39 3,068,174 12/1962 Pelton et al. 252-39 3,068,175 12/1962 Roach et al 252-39 3,079,341 2/1963 Coons et a1. 252-41 3,117,087 1/1964 McCormick et a1 252-41 DANIEL E. WYMAN, Primary Examiner. I. VAUGHN, Assistant Examiner. 

1. IN A PROCESS FOR PREPARING A SOAP THICKENED GREASE COMPRISING THE STEPS OF SAPONIFYING A SAPONIFIABLE FATTY ACID MATEIAL WITH A METAL BASE IN THE PRESENCE OF AT LEAST A PORTION OF THE LUBRICATING OIL CONTAINED IN THE GREASE, HEATING THE GREASE MIXTURE THUS OBTAINED AT A HIGHER TEMPERATURE BELOW THE MELTING POINT OF THE SOAP AND FINALLY COOLING THE GREASE MIXTURE AND ADDING ANY ADDITIONAL LUBRICTING OIL EMPLOYED IN THE GRASE, THE IMPROVEMENT WHICH COMPRISES INTIALLY PROVIDING A MIXTURE OF LUBRICATING OIL AND SAPONFIABLE MATERIAL AT AN ELEVATED TEMPERATURE SUFFICIENT TO OBTAIN A REACTION BETWEEN THE SAID SAPONIFIABLE MATERIAL AND SAID METAL BASE, AND CARRYING OUT THE SAPONIFICTION BY CONTINUOUSLY WITHDRAWING A MINOR STREAM FROM A MAINTAINED BODY OF THE SAID MIXTURE IN A GREASE MAKING ZONE, CONTINUOUSLY ADDING TO THE SAID WITHDRAWN STREAM A SOLUTION OF METAL BSE IN A LIQUID WHICH IS VAPORIZABLE AT A TEMPERATURE EMPLOYED IN THE GREASE MAKING PROCESS, SUBJECTING THE RESULTING COMBINED STREAM TO TURBULENT MIXING AND THEN RETURNING IT TO THE SAID MAINTAINED BODY OF SAPONIFIABLE MATERIAL AND OIL MIXTURE, SAID SOLUTION OF METAL BASE BEING ADDED AT A RATE SUCH THAT THE RATIO OF THE RATE OF RECIRCULATION OF THE SAID MIXTURE OF LUBRICATING OIL AND SAPONIFIABLE MATERIAL TO THE RATE OF ADDITION OF THE SAID METAL BASE SOLUTION IS AT LEAST ABOUT 10:1.
 8. THE PROCESS OF CLAIM 1 WHEREIN THE SAID SAPONIFICATION MATERIAL COMPRISES AT LEAST ABOUT 50 PERCENT BY WEIGHT OF A HYDROXY FABRIC ACID MATERIAL. 